User's Manual

Appendix C - IDU Functionality
The following figure illustrates the functionality of an IDU.
The circuits of the Ethernet interface and the HSI module together with Digital Multiplexer (DATA
MUX), Digital Modem (DSP block), Central Processing Unit (CPU) and the Analog signal
processing block are the essential functional blocks of the IDU.
Data is first processed by the Ethernet physical layer, followed by the HSI interface. The
processed data is then directed to the Data Multiplexer for further processing. Digital modem
then adds synchronization marks, Forward Error Correction (FEC) to the data stream and creates
a digitally modulated signal, which is directed to the Analog signal block for further processing. All
these parts are interconnected inside the device with high-speed bus and are controlled by the
CPU. This block is also accessible via management interfaces and allows the user to configure
all the settings both locally and remotely through the IP interface on the IDU.
Digital Multiplexer (block DATA MUX), from a user's perspective is divided into two parts:
• RFI: Processes the data coming into the modem from HSI and Ethernet
• HSI: Process the data coming from the HSI module
RFI is a digital multiplexer (based on Packet Based Priority System (PBPS)) which creates a
single data stream for the modem block containing all the permitted user input data. The data
source for digital multiplexer are the signals from HSI interface, Ethernet data and data from the
internal BER tester. System PBPS first transmits the data with the high priority and than with the
low priority - from Ethernet block and from internal BER tester. Thus, prioritizing the data
transmission helps to dynamically reduce data transmission rate, depending on the available
overall transmission capacity.
Tsunami™ GX800 Installation and Management Guide 74
Figure 50: Block Diagram of the IDU